Detecting instants of injection, for example in checking the phases of a multi-line fuel injection pump

Abstract

 Apparatus for detecting instants of injection of fuel or test fluid through an injector of a fuel injection pump for an internal combustion engine, comprising an injector block (19) defining a plurality of cavities (46). These cavities (46) receive the nozzle ends (50) of the fuel injectors (18) of the different lines. Pressure sensors (56) are arranged in communication with the cavity interiors to detect changes in pressure therein.

Description

[0001] The present invention relates to apparatus for detecting instants of injection of fuel or test fluid through an injector of a fuel injection pump for an internal combustion engine, comprising a sensor arranged to detect instants when fuel or test fluid is injected through the nozzle end of such a fuel injector when the apparatus is in use.

[0002] In a previously proposed method of checking the phases of a multi-line fuel injection pump, respective proximity transducers are positioned over the needles of the injectors to detect when each needle is lifted by test oil pumped through the injector by the associated pump element. This method suffers from the disadvantage that a sensor has to be tailor-made for each of the various different types of injectors at present in use.

[0003] An aim of the present invention is to provide apparatus which is less susceptible to this disadvantage.

[0004] Accordingly, the present invention is directed to apparatus in accordance with the opening paragraph of the present specification, in which the apparatus further comprises a part defining a cavity which serves, when the apparatus is in use, to receive such a nozzle end, and in that the sensor is a pressure sensor arranged, in relation to the cavity, to detect a change in pressure transmitted through the cavity interior following such injection.

[0005] There may be a plurality of such cavities and a sensor for each one, and phase-angle checking means connected to the sensors to enable the apparatus to provide a check on the phase angles of the different lines of a multi-line fuel injection pump.

[0006] Each pressure sensor may comprise a piezogenerative crystal. The Applicants have found surprisingly, and contrary to the recognised teaching in the art hitherto, that a very sharp and clear leading edge of the signal, representing commencement of injection, is obtainable if the crystal is not clamped in position, that is to say if it is held loosely in the sensor.

[0007] An example of apparatus in accordance with the present invention is illustrated in the accompanying drawings, in which:-

Figure 1 shows a perspective view of the system incorporated in apparatus which also provides a volumetric measurement of test fluid which is pumped through the injector under test;

Figure 2 shows, on a larger scale, an axial-sectional view of a part of the dynamic phasing system shown in Figure 1;

Figure 3 shows an axial-sectional view, on a larger scale still, of a component which is shown in Figure 2;

Figure 4 is a diagram of part of the electrical circuitry of the system shown in Figure 1;

Figure 5 is a block circuit diagram of electronic circuitry of the system shown in Figure 1; and

Figure 6 shows a series of graphs which diagrammatically represent electrical voltage values plotted against time at various points in the electronic circuitry shown in Figure 5.

[0008] The apparatus shown in Figure 1 is a dynamic phasing system and comprises a test bench 10 on which is mounted a multi-line fuel injection pump 12 with a number of individual pump elements 14, one for each line. In the fuel injection pump illustrated, there are six lines, and accordingly there are six individual pump elements. Respective feed pipes 16 lead away from the pump elements 14 to respective injectors 18 held in an injector block 19 of the apparatus. The illustrated injector block 19 is capable of holding up to 12 injectors, although it is not necessary to use all of these during one testing procedure, and indeed in the illustrated apparatus only six are in use. However, it would be possible for the system to test another four or six-line injector fuel pump simultaneously with the one illustrated.

[0009] Leads 20 connect respective pressure sensors (not shown in Figure 1) associated with each injector mount of the injector block 19 to a junction box 22. Each lead 20 is connected to a corresponding conductor in a ribbon cable 24 which extends from the junction box 22 to a selector box 26. This has two signal output lines carried by a single lead 28 to a printed circuit board 30.

[0010] The system also includes a pulse-generating wheel 32 which is rotationally fast with the drive shaft of the injector pump 12. The pulse-generating wheel 32 is magnetically or optically marked at points around its cicumference which have equal

[0011] angular spacing, and in this particular case it has one hundred and twenty marks spaced apart at three degree intervals. A magnetic or optical pick-up head 34 is clamped at a fixed position adjacent to the periphery of the wheel 32 so that a pulse signal is transmitted along the output lead 36 from the pick-up head 34 to the printed circuit board 30 every time one of the magnetic or optical marks on the wheel 32 passes the head 34. This enables the electronic circuitry on the printed circuit board 30, to be described in greater detail hereinafter, to measure the angle through which the drive shaft of the pump 12 rotates in between signals supplied successively by any two of the pressure sensors as selected by the selector box 26. A display bus lead 38 connected between the printed circuit board 30 and a digital display 40 allows this measurement to be indicated visually.

[0012] A signal from a pressure sensor indicates commencement of injection by the adjacent injector. The angular measurement displayed on the digital display 40 therefore shows the phase angle between two successive commencements of injection of the two lines of the fuel pump 12 selected at the selector box 26.

[0013] The manner in which a pressure sensor is used to detect the commencement of injection by an injector is shown in Figure 2. This shows that the injector block 19 has a cavity 46 for receiving the nozzle end of an injector 18. Although only one cavity 46 is illustrated in Figure 2, the injector block 19 has twelve such cavities to enable up to twelve injectors 18 to be mounted on the injector block 19. The injector 18 is held by a clamp (not shown) with its nozzle 50 within the cavity 46 and a seal formed all the way round a shoulder of the injector 18 and an upper end of the cavity 46 by means of a collar 51 and 0-ring seals 52. As shown in Figure 2, the clamp (not shown) is used to urge the injector 18 downwardly to such an extent that the normally circularly cross-sectioned 0-rings are squashed into a triangular cross-section defined by the surfaces which they contact. The system is therefore a closed chamber measuring system although it could possibly be an open chamber measuring system with the illustrated devices and circuitry. The only outlet from the chamber 46 is via an outlet port 54, and a back-pressure valve (not shown) is arranged downstream of the outlet to ensure a minimum of pressure of fluid within the chamber 46. This pressure ensures that any free air or gas created as tiny bubbles in the test oil due to turbulence following injection is re-absorbed by the test oil. A pressure sensor 56 is mounted on the injector block 19 so as to be in communication with the cavity 46. Although only one pressure sensor 56 is shown in Figure 2, it will be appreciated that there are twelve in the system altogether, one for each cavity 46.

[0014] When test fluid is shot through the nozzle 50, a pressure wave thus generated at the commencement of injection is transmitted through the test fluid in the cavity 46 to the pressure sensor 56, whereupon an electrical signal is generated by the pressure sensor indicative of the commencement of injection. The electrical signal occurs slightly after the actual commencement of injection, but the delay corresponds to approximately 1/5 degree rotation of the pump drive shaft at appropriate speeds of revolution thereof.

[0015] The structure of the pressure sensor 56 which enables it to generate an output electrical signal at the commencement of injection is illustrated in Figure 3. It comprises a mild steel housing 58 (although this could equally well be made of a synthetic plastics material such as nylon) clamped to a rigid mild steel end plate 60 by means of screws 62 (only one of which is shown in Figure 3). An interior space defined between the housing 58 and the end plate 60 houses two circularly shaped pieces of copper clad board 64 which lie parallel to one another with their copper clad faces towards one another. A lead zirconate titanate ceramic piezogenerative crystal 66 is sandwiched between the copper clad faces of the pieces of board 64. A light aluminium piston 68 of the sensor has a flanged head 70 positioned adjacent to the outer face of the board piece 64 which is further from the end plate 60, most of the piston 68 projecting outwardly from the sensor through a central hole in the housing 58. The piston 68 is restrained from movement away from the rest of the sensor by virtue of the flange head 70 engaging an inside shoulder surface of the housing 58. Two conductors of an output lead 76 from the sensor are soldered respectively to the copper clad surfaces of the board pieces 64 at solder points 78.

[0016] The dimensions of the interior space defined between the housing 58 and the end plate 60 are slightly greater than that required to accommodate the board pieces 64, the crystal 66, and the flanged piston head 70. This means that' the crystal 66 is retained loosely in the sensor. In this respect, the crystal can be said to be decoupled, or free- floating. Although this is contrary to the recognised teaching in the art of piezogenerative crystals, it has surprisingly been found to create a sharper and more distinctive leading edge to the signal which represents the commencement of injection.

[0017] The pressure sensor 56 is clamped to the injector block 19 with its piston 68 extending through a bore in the injector block 19 leading to the cavity 46 so that the free end of the piston 68 is in contact with the test fluid in the cavity 46 when the system is in use. The piston 68 has a neck portion 72 around which extends an 0-ring 75 that forms a seal between the piston 68 and the interior surface of the bore through which the piston 68 extends.

[0018] It will be appreciated therefore, that when the pressure sensor 56 is mounted for operation as shown in Figure 2, the components within the sensor do not rattle about, because of the pressure of the test fluid in the cavity 46 acting on the piston 68 to urge it inwardly towards the rest of the sensor, and also because of the damping effect of the 0-ring 75.

[0019] At the commencement of injection, when test fluid is shot through the nozzle 50 into the cavity 46, the pressure wave set up strikes the free end of the piston 68 which is thereby urged towards the board pieces 64 and the crystal 66. Because of the intrinsic properties of the crystal 66, the shock of sudden stress which it thereby experiences, being rapidly squashed between the board pieces 64 which in turn are squashed between the piston 68 and the end plate 60, causes the crystal to produce an electrical voltage or electromotive force across its main faces. This voltage is applied across the copper cladding of the two board pieces 64, and consequently across the two conductors of the output lead 76 of the sensor.

[0020] The electrical circuitry of the system between the various pressure sensors 56 and the printed circuit board 30 is shown in Figure 4. In this Figure, only four pressure sensors are shown for the sake of clarity and simplicity, but the actual manner in which the twelve pressure transducers of the system shown in Figure 1 are connected to the printed circuit board 30 is precisely analogous, and will be readily apparent from Figure 4 and the ensuing description.

[0021] The two conductors of each lead 76 (not shown in Figure 4) are connected to two conductors of a corresponding one of the leads 20. Each of the conductors in the lead 20 are connected at a junction box 22 to respective conductors in the ribbon cable 24. This ribbon cable 24 is represented by very short lengths of line in Figure 4. Every alternate conductor (not shown) of the ribbon cable 24 is grounded so that the conductors which are used to transmit electrical signals are screened from one another. At the selector box 26, one of the two ribbon cable conductors which are connected to each lead 20 is connected to a common conductor 74, and the other conductor connected to each lead 20 is connected to a corresponding terminal 76 of a datum line selector switch 78 and also to a corresponding terminal 80 of a phasing line selector switch 82. The other side of the datum line selector switch 78 is connected to a datum line conductor 84, and the other side of the phasing line selector switch 82 is connected to a phasing line conductor 86. The common conductor 74,datum line conductor 84 and phasing line conductor 86 are connected to the printed circuit board 30 via the connecting leads.28.

[0022] It will be appreciated from the foregoing description that the selector box 26 can be used to send the output signal of any selected pressure sensor 56 along the datum line conductor, and the output signal from any selected pressure sensor along the phasing line conductor 86. Thus, by observing the various connections, the particular cavity 46 which receives the injector 18 corresponding to the datum line of the injector pump 12 under test, which is usually the line from the first of the individual pump elements 14 in the pump 12, may be ascertained. The datum line selector switch 78 is then rotated to the corresponding setting, so that the signals from the pressure sensor associated with the datum line are connected to the datum line conductor 84. The pnasing line selector switch 82 may then be rotated as desired to a position corresponding to the particular line of the pump 12 the phase of which in relation to the datum line is to be measured.

[0023] The electronic circuitry on the printed circuit board 30 is shown in Figure 5. It comprises a percentage of signal peak detector 88 having its input connected to receive signals propagated along the datum line conductor 84. The porcontbgo of nignnl ponk dntootor 08 10 conolructod to memorise the average value of recent maximum peak voltage values received at its input, and to set a threshold value at a certain percentage of that peak value, for example 60%. It will produce a pulse signal each time this threshold value is exceeded, or each time the input voltage rises through that value. The stored value of maximum peak voltage is continuously up-dated by the detector 88. The output of the detector 88 is connected to a shaft speed enable circuit 90, a signal missing detector 92 in the form of a re-triggerable monostable multivibrator, and a lockout-period circuit 94.

[0024] A percentage of signal peak detector 95, having exactly the same structure as the detector 88, is connected to receive signals from the phasing line conductor 86. Its output is connected to a signal missing detector 96, having the same structure as the detector 92, and a further lockout-period circuit 98 having exactly the same structure as the circuit 94. A phase angle detector 100, comprising a bistable multivibrator, is connected to receive signals from the two lockout-period circuits 94 and 98,so that it is switched on by a leading edge of a signal from the circuit 94, and switched off by a leading edge of a signal from the circuit 98. The detector 100 produces an output signal for the duration of the time for which it is switched on. This output signal is received by an enabling input to a four decade BCD counter 102. This counter 102 also receives pulses emitted from a phase- locked-loop multiplier 104 connected to receive signals from the pick-up head 34 via the lead 36 and to give thirty times more output pulses than the number of input pulses it receives. In the present system there are therefore three thousand six hundred pulses emitted by the multiplier 104 for every turn of the drive shaft of the injector pump 12. The pulses from the counter 102 are passed to a multiplexer 106 for display driving, the multiplexer 106 being connected to the digital display 40 via the display bus lead 38. The multiplexer 106 is updated every half second by an oscillator 108.

[0025] The electronic circuitry shown in Figure 5 also comprises a display zeroing circuit 110 connected to receive outputs from either one of the signal missing detectors 92 and 96 and to cause the counter 102 to output a zero value in the event that it receives a signal from either detector 92 or 96.

[0026] The graphs shown in Figure 6 show the voltage levels of points (a) to (h) respectively of the circuitry shown in Figure 5 during operation of the apparatus. From the graphs it can readily be seen that the counter 102 is only enabled for the duration of the output signal (g). Therefore, only those pulses appearing at the output to the counter 102 between the times t₁ and t₂₉ and then again between the times t₃ and t₄₁ are passed through to the multiplexer 106. The latter is connected to the digital display 40 via the display bus 38 so that the display 40 shows a measurement of the phase angle between the phasing line and the datum line in 1/10ths of a degree.

[0027] Because the illustrated system enables the commencement of injection to be measured precisely, and more particularly it can do this in a dynamic test with the actual injectors which are used with a given engine rather than some other test injectors, the system can be used^;to set the crank shaft of the engine with the correct angular position in relation to the pump drive shaft with greater ease and increased precision. Usually, the angular setting is such as to obtain commencement of injection relative to top dead centre.

Claims

1. Apparatus for detecting instants of injection of fuel or test fluid through an injector of a fuel injection pump (12) for an internal combustion engine, comprising a sensor (56) arranged to detect instants when fuel or test fluid is injected through the nozzle end (50) of such a fuel injector (18) when the apparatus is in use, characterised in that the apparatus further comprises a part (19) defining a cavity (46) which serves, when the apparatus is in use, to receive such a nozzle end (50), and in that the sensor is a pressure sensor (56) arranged, in relation to the cavity (46), to detect a change in pressure transmitted through the cavity interior following such injection.

2. Apparatus according to claim 1, characterised in that the said part (19) defines a plurality of cavities (46), and in that their are a plurality of such sensors (56), one for each cavity, and phase-angle checking means (30) connected to the sensors (56) to enable the apparatus to provide a check on the phase angles of the different lines of a multi-line fuel injection pump (12).

)3. Apparatus according to claim 1 or claim 2, characterised in that the or each pressure sensor (56) provides a signal in dependence upon changes in pressure rather than upon actual pressure.

4. Apparatus according to claim 3, characterised in that the or each pressure sensor (56) comprises a piezogenerative crystal (66) retained loosely in the sensor.

5. Apparatus according to claim 2, characterised in that the apparatus further comprises pump drive-shaft rotation monitoring means (34), wherein the phase-angle checking means (30) comprises electronic circuitry connected to receive output signals from the pressure sensors (56) and the monitoring means (34) and to provide therefrom a check on the phase angles, and wherein selector switch means (76 and/or 80) are connected between the pressure sensors (56) and the electronic circuiry (30) to selectively allow output signals from the pressure sensors (56) to pass to the electronic circuitry (30).

6. Apparatus according to claim 5, characterised in that the electronic circuitry (30) comprises a signal )detector (95) which is triggered when it receives an input signal that is beyond a threshold value, and lockout means (98) connected to receive output signals from the detector (95) and to provide a lockout signal for a predetermined interval after it first receives a signal from the detector

7. Apparatus according to claim 6, characterised in that means (36) are provided to set the predetermined interval to correspond to a given angle of rotation of the drive shaft rather than a given absolute time period.

8. A method of checking phase angles of different lines of a multi-line fuel injection pump (12) for an internal combustion engine, characterised by (a) inserting the nozzle end (50) of the fuel injectors (18) of the different lines into respective cavities (46), (b) detecting instants at which changes in pressure occur in the cavities (46) by means of respective pressure sensors (56) arranged to detect pressure changes transmitted through the cavity interiors owing to fluid being shot through the nozzles (50) of the injectors (18), and (c) using those detected instants to provide a check on the phase angles of the different lines.

9. For use in detecting the commencement of injection of fluid through an injector (18) of a line of a fuel injection pump (12), a pressure sensor (56) characterised by a piezogenerative crystal (66) retained loosely in the sensor (56).

10. For use in checking phase angles of different lines of a multi-line fuel injection pump (12) for an internal combustion engine, detecting apparatus characterised by (a) means (56) for detecting a particular instant in the pumping cycle as it occurs in each line, (b) means (34) for monitoring rotation of a drive shaft of the pump (12), (c) electronic circuitry (30) connected to receive output signals from the detector means (56) and the monitoring means (34) and to provide therefrom a check on the phase angles, and (d) selector switch means (76 and/or 80) connected between the detector means (56) and the electronic circuitry (30) to selectively allow output signals from the detector means (56) to pass to the electronic circuitry (30).

Drawing